1. Field of the Invention
The present general inventive concept relates generally to a power supply apparatus (power supply) and an electronic device including the power supply. More particularly, the present general inventive concept relates to a power supply to avoid a potential change of a ground power and enhancing EMI characteristic by reducing a length of a harmonic current path, and an electronic device including the power supply.
2. Description of the Related Art
In general, electronic devices performing a certain function with electronic elements, for example, image forming apparatuses for printing image on a printing medium such as printers, copiers, multifunction peripherals (MFP), and fax machines, receive a commercial alternating current (AC) power from outside and convert the AC to a driving power of a potential level suitable for each electronic device. To execute preset functions of the electronic devices, the power supply is required for converting the commercial AC power to the driving power.
Of the power supplies, a Switching Mode Power Supply (SMPS) is mostly frequently used. The SMPS switches DC power, which is obtained by rectifying and smoothing the commercial AC power input from the outside, to a certain high frequency, e.g., to a high frequency of about 100 kHz to convert to a desired voltage using a transformer in high efficiency.
Typically, the power supply such as SMPS needs a ground power together with the commercial AC power to provide a ground potential to each element of the power supply. Accordingly, a ground part for supplying the ground power is included in the power supply.
The layout pattern of the ground part is formed as large as possible to ensure a stable potential level of the ground power, that is, to prevent a change of the potential level of the ground power. To supply the stable ground power to the internal elements, the internal elements are commonly grounded to the ground part as constructed above.
However, when the commercial AC power of a sine wave is applied to the internal elements of the electronic device, every internal device through which the current flows acts as the source of harmonic current. As the internal devices are commonly grounded to the ground part, the current path of the harmonic current is lengthened. Accordingly, a long current path may increase noise components and noise problems. The noise increase may cause deterioration of an electromagnetic interference (EMI) characteristic of the power supply.
Therefore, to avoid the degradation of the EMI characteristic, what is needed is a method to reduce a harmonic current path and to maintain a stable potential of the ground power.